The invention is concerned with the field of fiber optical communication architectures and network systems, and the problems of optically switching fiber-carried light signals between input and output fibers in high speed optical communication networks and the like, with more particular concern for optical cross-connect switching and control between fiber optical input and output (I/O) bundle arrays.
The switching of signal light beams between optical fiber bundles carrying data optical I/O cards in communication networks and systems is currently being addressed with the aid of optical microelectric-electromechanical devices (MEMS or MOEMS) carrying tiltable micro-mirrors orientable by electrical signal control to deflect incident light beams along desired pathsxe2x80x94switching the output light from input fibers via reflection from the micro-mirrors to predetermined fibers in an output fiber bundlexe2x80x94the so-called optical cross-connect switching mentioned above.
Examples of such MEMS devices are disclosed, for example, in U.S. Pat. Nos. 6,052,498; 6,147,876; 6,150,724; and 6,151,173; and details of such optical switching systems are described, for example, in the following references:
[1] xe2x80x9cFlexible, Modular, Contact Fiber Optic Switchxe2x80x9d, Slater, et al., Xros Patent Application, WO 00/20899. Apr. 13, 2000;
[2] xe2x80x9cSensing Configuration for Fiber Optic Switch Control Systemxe2x80x9d, Laor, et al., Astarte Fiber Networks, Inc., U.S. Pat. No. 6,097,858, Aug. 1, 2000;
[3] xe2x80x9cOptical MEMS for Lightweight Networksxe2x80x9d, David Bishop, SC233, SPIE Photonics East, Nov. 8, 2000
In general, such free-space optical switches steer the input light from any one of input fibers to any one of the output fibers. The number of input fibers and output fibers can range from tens to thousands. The principal challenges to controlling the light are providing for:
quickly moving one or multiple light beams from one location to another without disturbing the existing connections;.
fine adjusting of the light beam so that the beam is precisely placed into the optimal coupling range of the output fiber, so that the optical signal loss due to the coupling can be reduced to minimalxe2x80x94this loss being the major contributor to the total insertion loss of the optical switch;
precisely maintaining the connections despite possible mechanical or thermal disturbances;
establishing multiple connections simultaneously as requested by higher level provisioning software and within certain prescribed ranges;
adapting to the switch device architecture, as by providing the micro-mirror array chips with on-chip actuation and sensing circuitry; and
minimizing the space and computation power requirements for off-chip signal processing and control systems.
In the implementation of, for example, the optical switches of the above-cited Slater et al reference [1] and other similar prior art systems, electrical signal feedback circuits for establishing precise mirror position are widely used.
A piezoresistive sensing mechanism is generally provided on the torsional mirror support to measure position of the mirror. This sensing signal is fed to an error amplifier with a command input from digital signal processor a (DSP)-controlled digital analog controller (DAC). The error signal is fed through the analog controller to control the actuation or control voltage signal orienting the mirror. Problems and limitations with this electrical feedback approach, however, arise from the facts that the controller is implemented in analog components which are not flexible; the controller is not scalable because each mirror needs its control; and the DSP is also not scalable because it is tied to the controller all of the time.
Resort has therefore been taken, as described in the Bishop reference [3] above, to the use of external optical feedback without using such on-chip electrical feedback signalsxe2x80x94i.e. using only port card optical power feedback. Since such involve a very slow loop, however, this poses extremely high requirements on MEMS design, in that the resonant frequency has to be much higher than the disturbance. The optical power feedback from the VO cards, furthermore, cannot give directional information. This thus requires extra time and computation power to adjust the mirror beam positions. While additional optical sensing schemes can be built into the optical box as in the Bishop proposal, this further increases the complexity of the optical box and adds more variables to control, i.e. the relative positions and alignment of the optical sensing elements in the optical box.
The present invention, on the other hand, through a novel use of intermediate node monitoring and with the use of test and real traffic data path switching, has admirably overcome the above-described and other limitations of such prior art techniques, as will later be more fully explained.
An object of the present invention, accordingly, is to provide a new and improved approach, method, architecture and system for optically switching light communication signals in fiber optic networks and the like that obviate the above and other prior art limitations and problems, and, indeed, provide for faster switching and optical path connections than have heretofore been available with optical cross-connect and other switching techniques.
A further object is to provide such improvement with novel working and test protection switching at intermediate nodes of the network that reduce overall connection setup time.
Other and further objects are stressed in the descriptions that follow and are more particularly pointed out in the appended claims.
In summary, however, from one of its broader viewpoints, the invention embraces in an optical path switching system wherein light beam data traffic is to be switched by MEMS orientable mirrors between a source node and a destination node through intermediate nodes having ingress and egress ports that are to be connected to set up the desired optical path connection between the source and destination nodes and under the control of a protocol control plane, a method of reducing the overall switch connection setup time while guaranteeing the integrity of the connection before the actual propagating of the data traffic from the source, that comprises, transmitting a test light beam from the ingress port of each intermediate node to a test detector at its egress port upon the identifying from the control plane of the ingress and egress port numbers of the node, thereby to set up and verify the integrity of an optical path connection therebetween; thereupon terminating the test light beam transmission; and then awaiting the subsequent propagation of the data traffic from the source along the setup-connected optical path to the selected destination node.
Preferred and best mode designs and embodiments are hereinafter explained in detail.